Audio tone signals employing multiple frequencies are provided to make selections for controlling circuits. The circuits providing these audio tone signals produce different audible frequencies which are paired in a variety of combinations to produce distinctive output pulses. The output pulses are transmittable to effect control of a system.
These discrete output pulses may control a system which provides character selection correlated to the distinctive output pulse. For example, the output pulses may be correlated to decimals 0-9.